(1) Field of the Invention
The present invention relates to a disk apparatus which reads data from and writes data onto a disk, wherein the disk is rotated by a rotating motor in accordance with a source power, and the source power supplied to the rotating motor is monitored.
(2) Description of the Prior Art
Magnetic disk drives such as hard disk drives have been connected to host computers for a purpose of storing information. Recently, hard disk drives with a smaller size and a lighter weight have been developed and put into practical use, and they can be housed in small-size personal computers. Certain personal computers of a handy type are powered by a battery, instead of by being plugged into an electric outlet.
For the personal computers mentioned above that are powered by the battery, it is desirable that power consumption of such disk drives during operation be minimized and a faster rotation of the disk by a rotating motor be realized with a source voltage supplied from the battery.
FIG. 1 shows a conventional magnetic disk unit 11. In FIG. 1, the magnetic disk unit 11 includes an actuator 12, an arm 13, and a head 14. The head 14 is connected to one end of the arm 13 via a supporting spring member 13a. The head 14 is placed onto a magnetic disk 20, and is movable in a radial direction of the disk as indicated by a two-dot chain line in FIG. 1.
The arm 13 has a base portion which is rotatably supported onto a pivot 15, and the arm 13 is rotatable around the center of the pivot 15. The arm 13 has a supporting portion 16 at the other end thereof opposite to the head 14, and a coil 17 is attached to the supporting portion 16. The arm 13, when rotated by an electromotive force induced in the coil 17, is supported on the supporting portion 16.
Two magnets 18a and 18b are secured to a frame of the magnetic disk unit 11 and arranged below the coil 17. The coil 17 and the magnets 18a and 18b constitute a voice coil motor (VCM). This VCM serves to rotate the arm 13 around the pivot 15 by a small angle so that the head 14 is moved to a selected one of the tracks of the disk 20.
The disk 20 is placed onto a spindle 19 of a spindle motor (not shown in FIG. 1), and is rotated at high speed around the spindle 19 by the spindle motor. Electric power from a printed circuit board 21 is supplied to the coil 17 via a flexible print sheet 22, and the arm 13 is rotated around the pivot 15 by the coil 17 so that the head 14 is moved in the radial direction of the disk 20 to the selected track of the tracks of the disk 20.
In a case of a disk apparatus which is housed in a small-size computer powered by a battery, the electric charge of the battery supplied to the spindle motor may be too little, and thus the disk apparatus may be subjected to a lack of electric energy to start the rotation of the spindle motor. In addition, the disk apparatus may be abruptly powered off when the rotation of the spindle motor is started. If this takes place, data stored in the disk or data stored in a battery-backup random-access memory of the computer may be lost.
In order to prevent the stored data from being lost due to such a malfunction, it is necessary to monitor the source power supplied to the disk apparatus before the rotation of the spindle motor is started.
FIG. 2 shows a conventional source power monitoring system. In FIG. 2, a control unit 31 is connected to a sleep control circuit 32 and an SPM controller 33, and the SPM controller 33 is connected to a spindle motor (SPM) 34 of a disk device. The control unit 31 outputs a command to the SPM controller 33 to control the start and stop of the rotation of the SPM 34. The sleep control circuit 32 serves to stop a supply of source power to a specific portion of the system when no access is given to the disk device over a predetermined period, in order to reduce the consumption power to a certain extent.
In the conventional source power monitoring system, a source voltage Vcc of a battery and a predetermined reference voltage V1 are input to a comparator 35, and the source voltage Vcc is compared with the reference voltage V1. The comparator 35 outputs a fail signal to the control unit 31 when the source voltage Vcc is lower than the reference voltage V1. When the fail signal from the comparator 35 is received, the control unit 31 powers down the disk device.
The reference voltage V1 mentioned above is a criterion to ensure a high source voltage level and prevent stored information from being lost due to an abrupt powering down.
Japanese Laid-Open Patent Application No. 5-137393 discloses a power supply voltage monitoring unit which monitors the level of a source voltage supplied to a disk device. Unlike the comparator 35 of the conventional source power monitoring system, this monitoring unit is used to detect whether a source voltage at the start of the rotation of the spindle motor is greater than a reference voltage. In the disk device disclosed in the above publication, the current of the source power is varied in response to the source voltage level. When the source voltage level is low, the time to initially accelerate the rotation of the spindle motor to a steady speed is prolonged by varying the current of the source power supplied to the spindle motor, in order to stabilize the rotating speed of the spindle motor and to ensure safe data recording and reproducing.
In the above conventional source power monitoring system, the disk device is powered down if the source voltage Vcc is below the reference voltage V1. However, a great source current must be supplied from the battery to the spindle motor at the start of the rotation of the spindle motor. Thus, the above conventional source power monitoring system hardly reduces the consumption power of the disk device at the start of the rotation of the spindle motor.
In the above publication, an error in the source power of the disk device, if any, can be detected by a source power monitoring system when the voltage from the source power is lowered below a reference voltage. There is a problem, however, that unless the source voltage is lowered below the reference voltage, the system does not detect a small voltage fluctuation of the source power as being an error. In addition, there is a problem that the system cannot quickly transfer an error notification concerning the source power fluctuation to a host computer when the small voltage fluctuation of the source power is detected.
In order to prevent the above-described problems wherein information stored in the disk apparatus could be lost, it is desirable to quickly transfer an error notification signal to the host computer in response to a small voltage fluctuation, so that the notification of a defective battery is immediately addressed to the host computer.